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The rapidly evolving microbiome science has revealed a growing number of possibilities by which the gut microbiome can influence human health and disease, and by which microbiome-targeted manipulations could be effective treatments for a variety of chronic disorders. However, while the majority of these possibilities are primarily supported by studies in laboratory mice, and have not been translated into human therapies or diagnostics, microbiome science both in animal models and epidemiological studies has provided a wealth of evidence supporting the close link between a healthy diet (largely plant-based, devoid of ultra-processed components, low in sugar), a healthy microbiome and human health.

The simplest and best supported dietary advice I give to my patients is to eat what is best for their microbes, e.g. a largely plant-based diet with a high variety of plant-based and fermented foods. Such a microbiome-targeted diet will automatically be optimal for human health as well.

“…it underscores the benefits of plant-based foods and the drawbacks of ultra-processed ones…”

A comprehensive overview of dietary guidelines in relation to the gut microbiome, can be found in a review article by A Armet and Jens Walter from the APC Ireland at the University of Cork, published in the prestigious journal Cell Host & Microbes in 2022. This review supports the integral role of diet in chronic disease and health promotion. It suggests that while the great majority of dietary recommendations align with findings from microbiome research, there is a need for deeper integration of these insights into national dietary guidelines. Highlighting consistencies across international dietary advice, it underscores the benefits of plant-based foods and the drawbacks of ultra-processed ones, emphasizing the microbiome’s interaction with various dietary components and its impact on health.

Microbiome science has taught us that not all plant-based diets are the same, or have the same benefit for the well-being of our gut microbes, gut health and overall health. For example, a person who restricts his/her diet to eating carrots, rice and potatoes 7 days a week, will not get much health benefits from being a vegetarian. As I have pointed out repeatedly, it is not only WHAT you eat, but also WHAT VARIETY of plant-based foods you consume, and HOW these foods are grown.

“…by addressing the role of different types of plant-based diets, as well as the characteristics of the studied population.”

A research paper titled, “Plant-based diets and the incidence of cardiovascular disease: the Million Veteran Program” with lead author Yanping Li and published in the British Medical Journal Nutrition, Prevention & Health in 2023, adds more detail to the recommendations of a largely plant-based diet by addressing the role of different types of such diets, as well as the characteristics of the studied population.

While plant-based diets have been associated with lower risks of coronary heart disease, type 2 diabetes, metabolic syndrome, cognitive decline and certain cardiometabolic risk factors in general populations, less is known about their impact on the veteran population in the United States. This demographic presents unique challenges and characteristics, including higher prevalence of chronic health issues, unhealthy lifestyles, lower socioeconomic background and a high prevalence of chronic life stress compared to the general population. The study by Yanping Li and colleagues aimed to investigate the associations between different plant-based dietary patterns and the risk of cardiovascular disease within the Veterans Affairs (VA) Million Veteran Program (MVP), a vast and diverse cohort with comprehensive dietary and health record data.

The study utilized data from 148,506 MVP participants who were free of diabetes, cardiovascular disease, and cancer at baseline. Dietary intake was assessed using a standard Food Frequency Questionnaire (FFQ), which served as the basis for identifying two subgroups within the population consuming a plant-based diet. The three groups were characterized by a Plant-Based Diet Index (PDI), a healthful PDI (hPDI), and an unhealthful PDI (uPDI). Healthy plant food groups included whole grains, fruits, vegetables, nuts, legumes and tea/coffee. Less healthful plant food groups included fruit juices, sugar-sweetened beverages, refined grains, potatoes, and sweets/desserts. Animal-based food groups included animal fats, dairy, eggs, fish/seafood and meat (poultry and red meat). Cardiovascular disease (CVD) endpoints included non-fatal and fatal myocardial infarction and acute ischemic stroke tracked over a follow-up period of up to 8 years.

“…not only the amount of plant-based food somebody consumes, but also the quality of such foods.”

The study documented 5,025 CVD cases during the follow-up period. After adjusting for various confounding factors, a higher overall PDI was significantly associated with a lower risk of CVD, indicating that a plant-based diet, in general, could confer similar cardiovascular benefits to this Veteran population as had been shown previously for civilian populations. Not surprisingly, the healthy PDI group showed a strong inverse relationship with CVD risk (e.g. the higher individuals scored on the PDI, the lower their risk of CVD), underscoring that it is not only the amount of plant-based food somebody consumes, but also the quality of such foods. Conversely, the unhealthy PDI was positively associated with CVD risk, suggesting that not all plant-based diets are beneficial for cardiovascular health, particularly those that include higher quantities of less healthy plant foods.

“…diets rich in healthy plant foods for the prevention of CVD, consistent with dietary guidelines…”

This study highlights the potential cardiovascular benefits of plant-based diets among US veterans, a group that has not been the focus of much research in this area The study’s findings align with the broader literature, indicating protective effects of plant-based diets against CVD. Previous research in health professional populations has similarly identified the benefits of high-quality plant-based diets and the potential risks associated with diets high in less healthy plant foods. The findings support the promotion of diets rich in healthy plant foods for the prevention of CVD, consistent with dietary guidelines advocating for increased consumption of plant foods while reducing animal foods intake.

The study’s strengths include its large sample size, longitudinal design (rather than cross sectional assessments), and the use of validated dietary assessment tools. Even though not assessed in detail, the study results suggest that a healthy plant-based diet is not only beneficial for health professional populations, as studied extensively in the Nurses’ Health study, but also has identified the benefits of high-quality plant-based diets and the potential risks associated with diets high in less healthy plant foods.

The study expands the understanding by applying these insights to a veteran population, which is both unique and under-researched in nutritional epidemiology. However, limitations such as the correlational (rather than causal evidence) between diet and health, as well as the reliance on self-reported dietary data, which is notoriously unreliable, lower the strength of this study.

“… identified the key roles that the gut microbiome plays in mediating these health benefits.”

In summary, an ever-growing body of scientific data supports the benefit of a high quality largely plant-based diet for our health, and has identified the key roles that the gut microbiome plays in mediating these health benefits. As the reviewed results in veterans suggest, the benefits of such a diet are not contingent on the baseline characteristics of study populations.

There is no question that microbiome science will identify many more health and disease relevant diagnostic approaches, including the early identification of risk factors for diseases like Parkinson’s, Alzheimer’s disease and autism spectrum disorders, and will help to develop novel therapeutic approaches like genetic engineering of microbes, or of therapeutic cocktails of beneficial microbes for specific diseases.

However, for the foreseeable future, focusing on the implementation of dietary guidelines not just for the well to do, but also for disadvantaged populations, like veterans or populations of lower socio-economic status seems to be the most effective approach to prevent and treat many chronic diseases.